There is available a method of allowing a user to visually grasp the presence/absence of emphysema or an emphysema distribution in the lung field regions by observing the MPR image depicting the lung fields, which are obtained by imaging the chest region of an object using an X-ray computed tomography apparatus. There is also available a method of making an X-ray computed tomography apparatus display low CT value regions in color, which are extracted from the lung fields by performing threshold processing for CT values.